As a glass sheet bending apparatus for bending a glass sheet during the transfer of it, a roller-form conveyor is known. The roller-form conveyor is provided with roller assemblies each comprising a guide shaft bent preliminarily to have a predetermined curvature and a plurality of ring rollers attached rotatably to the guide shaft wherein the ring rollers are connected to each other, whereby the roller assemblies can be rotated by a power machine or a power transmitting means disposed at a side of guide shafts. The roller assemblies are arranged in parallel to thereby form a transferring path having a predetermined curvature. When a glass sheet heated to a temperature near the softening point is transferred on the transferring path, the heated glass sheet is bent by its own weight so as to meet the curved surface of the transferring path.
There are many numbers of examples as to structures of roller assemblies.
U.S. Pat. No. 4,311,509 discloses such structure that projections are formed at one side of ring rollers and grooves are formed at the other side of ring rollers wherein a projection formed in a ring roller is fitted to a groove formed in an adjacent ring roller, so that when a rotating force is given to a ring roller at an end, the rotating force is transmitting successively to other rollers whereby all ring rollers can be rotated around the guide shaft holding the ring rollers, as a whole.
U.S. Pat. No. 4,203,754 discloses a roller assembly comprising a flexible bellows type pipe made of stainless steel in which spirally screw-cut portions are formed. A plurality of collars are fastened with spaces to the bellows type pipe by means of the screw-cut portions. Slip pipes are inserted in the collars and are fitted to an outer periphery of a guide shaft. When bellows type pipes are rotated through the slip pipes, a glass sheet is transferred so that it is bent by its own weight along a predetermined curvature formed by the bellows type pipes.
JP-A-8-188431 discloses a roller assembly comprising a guide shaft bent preliminarily to have a predetermined curvature and coil springs fitted rotatably to an outer periphery of the guide shaft. When a rotating force is applied to an end of the coil springs, the coil springs are rotated integrally around the guide shaft.
JP-A-10-218629 discloses a roller assembly of a type that a plurality of ring rollers are fitted to a guide shaft bent preliminarily to have a predetermined curvature; annular ribs are formed at both sides of adjacent ring rollers, and flexible tubular members made of, for example, rubber are fitted to the annular ribs, wherein both ends of the flexible tubular members are connected to the annular ribs by screws so that adjacent ring rollers are connected to each other.
In the above-mentioned structures, however, it was necessary to prepare guide shafts for different kinds of articles having different curvatures because each guide shaft was preliminarily formed to have a predetermined curvature, whereby there was a problem of cost increase. Further, there was a problem that it took a long time for job changing because it was necessary to exchange rollers when a kind of article which has been produced was changed to another to be produced. This caused a reduction in productivity of curved glass sheets.
On the other hand, there is proposed a roller assembly allowing its curvature to have a predetermined value. This roller assembly has such a structure that a guide shaft having a form of coil spring holds thereon a plurality of ring rollers so that the guide shaft can be bent to have a predetermined curvature. This roller assembly uses a thick coil spring. Accordingly, when a glass sheet is bent to have a small radius of curvature R such as a radius of 1,000 mm, which is usable for, for example, a window glass for an automobile, it is difficult to use the roller assembly having a thick coil spring because a smaller radius of curvature is required. Use of a thinner coil spring causes a reduction of the stiffness of the coil spring and is apt to suffer influence by an external force, whereby there is a problem that accuracy in the shape of a bend-shaped glass sheet becomes poor.